Today many different types of plate heat exchangers exist and are employed in various applications depending on their type. Some types of plate heat exchangers are assembled from a casing that forms a sealed enclosure in which heat transfer plates that are joined are arranged. The heat transfer plates form a stack of heat transfer plates where alternating first and second flow paths for a first and a second fluid are formed in between the heat transfer plates.
For one type of plate heat exchangers, the so called central-port plate heat exchanger, each heat transfer plate has a central opening (central port) for the first fluid path. Fluid in the first fluid path enters a heat transfer plate at an inlet section of the central opening in the heat transfer plate, flows across the plate and leaves the plate at an outlet section of the same central opening. The outlet section is opposite the inlet section and a fluid separation device is inserted in the central opening for separating the fluid flow to the inlet section from the fluid flow from the outlet section. Thus, the same port is, by virtue of the separation device, used both as a fluid inlet and a fluid outlet for a fluid that flows over the heat transfer plate. Basically, the first fluid makes a 180° turn over the heat transfer plate, such that the first fluid leaves the plate at a location that is, as seen across the central opening, opposite the location where the first fluid entered the plate.
The second fluid enters the heat transfer plate at an inlet section of a periphery of the plate, flows across the plate and leaves the plate at an outlet section of a periphery of the plate, which outlet section is opposite the inlet section.
Obviously, the inlet and outlet for the first fluid are located between every second pair of plates while the inlet and outlet for the second fluid are located between every other, second pair of plates. Thus, the first and second fluid flows over a respective side of a heat transfer plate, in between every second pair of heat transfer plates. The plates of a plate pair that have an inlet and an outlet for the first fluid are sealed to each other along their entire peripheries while the plates of a plate pair that have an inlet and outlet for the second fluid are sealed to each other at their central openings.
Since the heat transfer plates are surrounded by the casing, the central-port plate heat exchanger may withstand high pressure levels in comparison with many other types of plate heat exchangers. Still, the central-port plate heat exchanger is compact, it has good heat transfer properties and may withstand hard operation conditions without breaking.
The joined heat transfer plates are sometimes referred to as a plate pack or a stack of heat transfer plates. The stack of heat transfer plates has a substantially cylindrical shape with an internal, central through hole that is characteristic for the central-port plate heat exchanger. The stack of heat transfer plates may be all-welded such that rubber gaskets may be omitted between heat transfer plates. This makes the central-port plate heat exchanger suitable for operation with a wide range of aggressive fluids, at high temperatures and at high pressures.
During maintenance of the central-port plate heat exchanger, the stack of heat transfer plates may be accessed and cleaned by removing e.g. a top or bottom cover of the shell and by flushing the stack of heat transfer plates with a detergent. It is also possible to replace the stack of heat transfer plates with a new stack that may be identical to or different from the previous stack as long as it is capable of being properly arranged within the shell.
Generally, the central-port plate heat exchanger is suitable not only for use as a conventional heat exchanger but also as a condenser or reboiler. In the two latter cases the shell may comprise additional inlets/outlets for a condensate, which may eliminate the need for a special separator unit.
The design of the central-port plate heat exchanger with its stack of heat transfer plates provides, as indicated, a combination of advantages and properties that are quite specific for the type. A number of embodiments of central-port plate heat exchangers have been disclosed, such as those found in patent document EP2002193A1. In comparison to several other types of plate heat exchangers, the central-port plate heat exchanger has a compact design and handles the flow of fluids well. However, it is estimated that the central-port plate heat exchanger may be improved in respect of its capability to more optimally direct the flow of fluids within the heat exchanger when it is operated, which would increase the thermal efficiency.